目前Go语言支持GDB、LLDB和Delve几种调试器。其中GDB是最早支持的调试工具，LLDB是macOS系统推荐的标准调试工具。但是GDB和LLDB对Go语言的专有特性都缺乏很大支持，而只有Delve是专门为Go语言设计开发的调试工具。而且Delve本身也是采用Go语言开发，对Windows平台也提供了一样的支持。本节我们基于Delve简单解释如何调试Go汇编程序。
3.9.1 Delve入门
首先根据官方的文档正确安装Delve调试器。我们会先构造一个简单的Go语言代码，用于熟悉下Delve的简单用法。
创建main.go文件，main函数先通过循初始化一个切片，然后输出切片的内容：
package main
import (
"fmt"
)
func main() {
nums := make([]int, 5)
for i := 0; i < len(nums); i++ {
nums[i] = i * i
}
fmt.Println(nums)
}
命令行进入包所在目录，然后输入dlv debug命令进入调试：
$ dlv debug
Type 'help' for list of commands.
(dlv)
输入help命令可以查看到Delve提供的调试命令列表：
(dlv) help
The following commands are available:
args ------------------------ Print function arguments.
break (alias: b) ------------ Sets a breakpoint.
breakpoints (alias: bp) ----- Print out info for active breakpoints.
clear ----------------------- Deletes breakpoint.
clearall -------------------- Deletes multiple breakpoints.
condition (alias: cond) ----- Set breakpoint condition.
config ---------------------- Changes configuration parameters.
continue (alias: c) --------- Run until breakpoint or program termination.
disassemble (alias: disass) - Disassembler.
down ------------------------ Move the current frame down.
exit (alias: quit | q) ------ Exit the debugger.
frame ----------------------- Set the current frame, or execute command...
funcs ----------------------- Print list of functions.
goroutine ------------------- Shows or changes current goroutine
goroutines ------------------ List program goroutines.
help (alias: h) ------------- Prints the help message.
list (alias: ls | l) -------- Show source code.
locals ---------------------- Print local variables.
next (alias: n) ------------- Step over to next source line.
on -------------------------- Executes a command when a breakpoint is hit.
print (alias: p) ------------ Evaluate an expression.
regs ------------------------ Print contents of CPU registers.
restart (alias: r) ---------- Restart process.
set ------------------------- Changes the value of a variable.
source ---------------------- Executes a file containing a list of delve...
sources --------------------- Print list of source files.
stack (alias: bt) ----------- Print stack trace.
step (alias: s) ------------- Single step through program.
step-instruction (alias: si) Single step a single cpu instruction.
stepout --------------------- Step out of the current function.
thread (alias: tr) ---------- Switch to the specified thread.
threads --------------------- Print out info for every traced thread.
trace (alias: t) ------------ Set tracepoint.
types ----------------------- Print list of types
up -------------------------- Move the current frame up.
vars ------------------------ Print package variables.
whatis ---------------------- Prints type of an expression.
Type help followed by a command for full documentation.
(dlv)
每个Go程序的入口是main.main函数，我们可以用break在此设置一个断点：
(dlv) break main.main
Breakpoint 1 set at 0x10ae9b8 for main.main() ./main.go:7
然后通过breakpoints查看已经设置的所有断点：
(dlv) breakpoints
Breakpoint unrecovered-panic at 0x102a380 for runtime.startpanic()
/usr/local/go/src/runtime/panic.go:588 (0)
print runtime.curg._panic.arg
Breakpoint 1 at 0x10ae9b8 for main.main() ./main.go:7 (0)
我们发现除了我们自己设置的main.main函数断点外，Delve内部已经为panic异常函数设置了一个断点。
通过vars命令可以查看全部包级的变量。因为最终的目标程序可能含有大量的全局变量，我们可以通过一个正则参数选择想查看的全局变量：
(dlv) vars main
main.initdone· = 2
runtime.main_init_done = chan bool 0/0
runtime.mainStarted = true
(dlv)
然后就可以通过continue命令让程序运行到下一个断点处：
(dlv) continue
> main.main() ./main.go:7 (hits goroutine(1):1 total:1) (PC: 0x10ae9b8)
2:
3: import (
4: "fmt"
5: )
6:
=> 7: func main() {
8: nums := make([]int, 5)
9: for i := 0; i < len(nums); i++ {
10: nums[i] = i * i
11: }
12: fmt.Println(nums)
(dlv)
输入next命令单步执行进入main函数内部：
(dlv) next
> main.main() ./main.go:8 (PC: 0x10ae9cf)
3: import (
4: "fmt"
5: )
6:
7: func main() {
=> 8: nums := make([]int, 5)
9: for i := 0; i < len(nums); i++ {
10: nums[i] = i * i
11: }
12: fmt.Println(nums)
13: }
(dlv)
进入函数之后可以通过args和locals命令查看函数的参数和局部变量：
(dlv) args
(no args)
(dlv) locals
nums = []int len: 842350763880, cap: 17491881, nil
因为main函数没有参数，因此args命令没有任何输出。而locals命令则输出了局部变量nums切片的值：此时切片还未完成初始化，切片的底层指针为nil，长度和容量都是一个随机数值。
再次输入next命令单步执行后就可以查看到nums切片初始化之后的结果了：
(dlv) next
> main.main() ./main.go:9 (PC: 0x10aea12)
4: "fmt"
5: )
6:
7: func main() {
8: nums := make([]int, 5)
=> 9: for i := 0; i < len(nums); i++ {
10: nums[i] = i * i
11: }
12: fmt.Println(nums)
13: }
(dlv) locals
nums = []int len: 5, cap: 5, [...]
i = 17601536
(dlv)
此时因为调试器已经到了for语句行，因此局部变量出现了还未初始化的循环迭代变量i。
下面我们通过组合使用break和condition命令，在循环内部设置一个条件断点，当循环变量i等于3时断点生效：
(dlv) break main.go:10
Breakpoint 2 set at 0x10aea33 for main.main() ./main.go:10
(dlv) condition 2 i==3
(dlv)
然后通过continue执行到刚设置的条件断点，并且输出局部变量：
(dlv) continue
> main.main() ./main.go:10 (hits goroutine(1):1 total:1) (PC: 0x10aea33)
5: )
6:
7: func main() {
8: nums := make([]int, 5)
9: for i := 0; i < len(nums); i++ {
=> 10: nums[i] = i * i
11: }
12: fmt.Println(nums)
13: }
(dlv) locals
nums = []int len: 5, cap: 5, [...]
i = 3
(dlv) print nums
[]int len: 5, cap: 5, [0,1,4,0,0]
(dlv)
我们发现当循环变量i等于3时，nums切片的前3个元素已经正确初始化。
我们还可以通过stack查看当前执行函数的栈帧信息：
(dlv) stack
0 0x00000000010aea33 in main.main
at ./main.go:10
1 0x000000000102bd60 in runtime.main
at /usr/local/go/src/runtime/proc.go:198
2 0x0000000001053bd1 in runtime.goexit
at /usr/local/go/src/runtime/asm_amd64.s:2361
(dlv)
或者通过goroutine和goroutines命令查看当前Goroutine相关的信息：
(dlv) goroutine
Thread 101686 at ./main.go:10
Goroutine 1:
Runtime: ./main.go:10 main.main (0x10aea33)
User: ./main.go:10 main.main (0x10aea33)
Go: /usr/local/go/src/runtime/asm_amd64.s:258 runtime.rt0_go (0x1051643)
Start: /usr/local/go/src/runtime/proc.go:109 runtime.main (0x102bb90)
(dlv) goroutines
[4 goroutines]
* Goroutine 1 - User: ./main.go:10 main.main (0x10aea33) (thread 101686)
Goroutine 2 - User: /usr/local/go/src/runtime/proc.go:292
runtime.gopark (0x102c189)
Goroutine 3 - User: /usr/local/go/src/runtime/proc.go:292
runtime.gopark (0x102c189)
Goroutine 4 - User: /usr/local/go/src/runtime/proc.go:292
runtime.gopark (0x102c189)
(dlv)
最后完成调试工作后输入quit命令退出调试器。至此我们已经掌握了Delve调试器器的简单用法。
3.9.2 调试汇编程序
用Delve调试Go汇编程序的过程比调试Go语言程序更加简单。调试汇编程序时，我们需要时刻关注寄存器的状态，如果涉及函数调用或局部变量或参数还需要重点关注栈寄存器SP的状态。
为了编译演示，我们重新实现一个更简单的main函数：
package main
func main() { asmSayHello() }
func asmSayHello()
在main函数中调用汇编语言实现的asmSayHello函数输出一个字符串。
asmSayHello函数在main_amd64.s文件中实现：
#include "textflag.h"
#include "funcdata.h"
// "Hello World!
"
DATA text<>+0(SB)/8,$"Hello Wo"
DATA text<>+8(SB)/8,$"rld!
"
GLOBL text<>(SB),NOPTR,$16
// func asmSayHello()
TEXT ·asmSayHello(SB), $16-0
NO_LOCAL_POINTERS
MOVQ $text<>+0(SB), AX
MOVQ AX, (SP)
MOVQ $16, 8(SP)
CALL runtime·printstring(SB)
RET
参考前面的调试流程，在执行到main函数断点时，可以disassemble反汇编命令查看main函数对应的汇编代码：
(dlv) break main.main
Breakpoint 1 set at 0x105011f for main.main() ./main.go:3
(dlv) continue
> main.main() ./main.go:3 (hits goroutine(1):1 total:1) (PC: 0x105011f)
1: package main
2:
=>3: func main() { asmSayHello() }
4:
5: func asmSayHello()
(dlv) disassemble
TEXT main.main(SB) /path/to/pkg/main.go
main.go:3 0x1050110 65488b0c25a0080000 mov rcx, qword ptr g [0x8a0]
main.go:3 0x1050119 483b6110 cmp rsp, qword ptr [r +0x10]
main.go:3 0x105011d 761a jbe 0x1050139
=>main.go:3 0x105011f* 4883ec08 sub rsp, 0x8
main.go:3 0x1050123 48892c24 mov qword ptr [rsp], rbp
main.go:3 0x1050127 488d2c24 lea rbp, ptr [rsp]
main.go:3 0x105012b e880000000 call $main.asmSayHello
main.go:3 0x1050130 488b2c24 mov rbp, qword ptr [rsp]
main.go:3 0x1050134 4883c408 add rsp, 0x8
main.go:3 0x1050138 c3 ret
main.go:3 0x1050139 e87288ffff call $runtime.morestack_noctxt
main.go:3 0x105013e ebd0 jmp $main.main
(dlv)
虽然main函数内部只有一行函数调用语句，但是却生成了很多汇编指令。在函数的开头通过比较rsp寄存器判断栈空间是否不足，如果不足则跳转到0x1050139地址调用runtime.morestack函数进行栈扩容，然后跳回到main函数开始位置重新进行栈空间测试。而在asmSayHello函数调用之前，先扩展rsp空间用于临时存储rbp寄存器的状态，在函数返回后通过栈恢复rbp的值并回收临时栈空间。通过对比Go语言代码和对应的汇编代码，我们可以加深对Go汇编语言的理解。
从汇编语言角度深刻Go语言各种特性的工作机制对调试工作也是一个很大的帮助。如果希望在汇编指令层面调试Go代码，Delve还提供了一个step-instruction单步执行汇编指令的命令。
现在我们依然用break命令在asmSayHello函数设置断点，并且输入continue命令让调试器执行到断点位置停下：
(dlv) break main.asmSayHello
Breakpoint 2 set at 0x10501bf for main.asmSayHello() ./main_amd64.s:10
(dlv) continue
> main.asmSayHello() ./main_amd64.s:10 (hits goroutine(1):1 total:1) (PC: 0x10501bf)
5: DATA text<>+0(SB)/8,$"Hello Wo"
6: DATA text<>+8(SB)/8,$"rld!
"
7: GLOBL text<>(SB),NOPTR,$16
8:
9: // func asmSayHello()
=> 10: TEXT ·asmSayHello(SB), $16-0
11: NO_LOCAL_POINTERS
12: MOVQ $text<>+0(SB), AX
13: MOVQ AX, (SP)
14: MOVQ $16, 8(SP)
15: CALL runtime·printstring(SB)
(dlv)
此时我们可以通过regs查看全部的寄存器状态：
(dlv) regs
rax = 0x0000000001050110
rbx = 0x0000000000000000
rcx = 0x000000c420000300
rdx = 0x0000000001070be0
rdi = 0x000000c42007c020
rsi = 0x0000000000000001
rbp = 0x000000c420049f78
rsp = 0x000000c420049f70
r8 = 0x7fffffffffffffff
r9 = 0xffffffffffffffff
r10 = 0x0000000000000100
r11 = 0x0000000000000286
r12 = 0x000000c41fffff7c
r13 = 0x0000000000000000
r14 = 0x0000000000000178
r15 = 0x0000000000000004
rip = 0x00000000010501bf
rflags = 0x0000000000000206
...
(dlv)
因为AMD64的各种寄存器非常多，项目的信息中刻意省略了非通用的寄存器。如果再单步执行到13行时，可以发现AX寄存器值的变化。
(dlv) regs
rax = 0x00000000010a4060
rbx = 0x0000000000000000
rcx = 0x000000c420000300
...
(dlv)
因此我们可以推断汇编程序内部定义的text<>数据的地址为0x00000000010a4060。我们可以用过print命令来查看该内存内的数据：
(dlv) print *(*[5]byte)(uintptr(0x00000000010a4060))
[5]uint8 [72,101,108,108,111]
(dlv)
我们可以发现输出的[5]uint8 [72,101,108,108,111]刚好是对应“Hello”字符串。通过类似的方法，我们可以通过查看SP对应的栈指针位置，然后查看栈中局部变量的值。
至此我们就掌握了Go汇编程序的简单调试技术。
(dlv) disassemble TEXT syscall.Syscall6(SB) src/syscall/asm_linux_arm64.s asm_linux_arm64.s:34 0x8dca0 fe0f1ff8 MOVD.W R30, -16(RSP) asm_linux_arm64.s:34 0x8dca4 fd831ff8 MOVD R29, -8(RSP) asm_linux_arm64.s:34 0x8dca8 fd2300d1 SUB $8, RSP, R29 asm_linux_arm64.s:35 0x8dcac b592ff97 CALL runtime.entersyscall(SB) asm_linux_arm64.s:36 0x8dcb0 e01340f9 MOVD 32(RSP), R0 asm_linux_arm64.s:37 0x8dcb4 e11740f9 MOVD 40(RSP), R1 asm_linux_arm64.s:38 0x8dcb8 e21b40f9 MOVD 48(RSP), R2 asm_linux_arm64.s:39 0x8dcbc e31f40f9 MOVD 56(RSP), R3 asm_linux_arm64.s:40 0x8dcc0 e42340f9 MOVD 64(RSP), R4 asm_linux_arm64.s:41 0x8dcc4 e52740f9 MOVD 72(RSP), R5 asm_linux_arm64.s:42 0x8dcc8 e80f40f9 MOVD 24(RSP), R8 => asm_linux_arm64.s:43 0x8dccc 010000d4 SVC $0 asm_linux_arm64.s:44 0x8dcd0 1ffc3fb1 CMN $4095, R0 asm_linux_arm64.s:45 0x8dcd4 43010054 BCC 10(PC) asm_linux_arm64.s:46 0x8dcd8 04008092 MOVD $-1, R4 asm_linux_arm64.s:47 0x8dcdc e42b00f9 MOVD R4, 80(RSP) asm_linux_arm64.s:48 0x8dce0 ff2f00f9 MOVD ZR, 88(RSP) asm_linux_arm64.s:49 0x8dce4 e00300cb NEG R0, R0 asm_linux_arm64.s:50 0x8dce8 e03300f9 MOVD R0, 96(RSP) asm_linux_arm64.s:51 0x8dcec b192ff97 CALL runtime.exitsyscall(SB) asm_linux_arm64.s:52 0x8dcf0 fd835ff8 LDUR -8(RSP), R29 asm_linux_arm64.s:52 0x8dcf4 fe0741f8 MOVD.P 16(RSP), R30 asm_linux_arm64.s:52 0x8dcf8 c0035fd6 RET asm_linux_arm64.s:54 0x8dcfc e02b00f9 MOVD R0, 80(RSP) asm_linux_arm64.s:55 0x8dd00 e12f00f9 MOVD R1, 88(RSP) asm_linux_arm64.s:56 0x8dd04 ff3300f9 MOVD ZR, 96(RSP) asm_linux_arm64.s:57 0x8dd08 aa92ff97 CALL runtime.exitsyscall(SB) asm_linux_arm64.s:58 0x8dd0c fd835ff8 LDUR -8(RSP), R29 asm_linux_arm64.s:1 0x8dd10 fe0741f8 MOVD.P 16(RSP), R30 asm_linux_arm64.s:1 0x8dd14 c0035fd6 RET asm_linux_arm64.s:1 0x8dd18 00000000 ? asm_linux_arm64.s:1 0x8dd1c 00000000 ? (dlv)
(dlv) regs PC = 0x000000000008dccc SP = 0x0000004000691560 X0 = 0x0000004000266000 X1 = 0x0000000000000004 X2 = 0x0000000000000000 X3 = 0x0000000000000000 X4 = 0x0000000000000000 X5 = 0x0000000000000000 X6 = 0x0000000000000001 X7 = 0x0000000000000004 X8 = 0x0000000000000049 X9 = 0x0000004000266010 X10 = 0x0000000000000002 X11 = 0x0000000000000200 X12 = 0x0000000000000003 X13 = 0x000000000000001b X14 = 0x0000000000000001 X15 = 0x0000000000000000 X16 = 0x0000000000000000 X17 = 0x0000000000000008 X18 = 0x0000000000000000 X19 = 0x0000000000000150 X20 = 0x0000ffffdaabb040 X21 = 0x0000000001504260 X22 = 0x0000004000002000 X23 = 0x0000000000000000 X24 = 0x0000000000000000 X25 = 0x0000000000000000 X26 = 0x0000004000691768 X27 = 0x0000000001503680 X28 = 0x0000004000001980 X29 = 0x0000004000691558 X30 = 0x000000000008dcb0